Tincture of iodine was first used as a topical disinfectant in 1839. Tincture of iodine and subsequent iodine compositions, like Lugol's solution, are topical irritants that stain human skin. The invention of povidone iodine in 1956 (U.S. Pat. No. 2,739,922), commonly referred to as "tamed" iodine, eliminated the topical irritancy associated with iodine but not the staining.
Povidone iodine contains very low (1-10 ppm) concentrations of molecular iodine (I.sub.2) and high concentrations of triiodide (I.sub.3.sup.-.apprxeq.10,000 ppm) and iodide (I.sup.-.apprxeq.5,000 ppm). Such compositions are referred to as "complexed" iodine. Complexed iodine generically refers to compositions wherein molecular iodine is complexed with organic molecules and/or iodide. Molecular iodine is complexed in order to increase shelf-life and reduce irritation. It is currently described in the literature and believed by those skilled in the art that molecular iodine is the iodine species responsible for epidermal irritancy and staining. By lowering the concentration of molecular iodine it is believed that the irritancy and staining of iodine is minimized.
Many inventions that rely upon complexed iodine have been made in the field of topical iodine compositions. Iodine is complexed by contacting a source of diatomic iodine (I.sub.2) with a polymeric material having large segments of polymeric residues derived from ethylene oxide, propylene oxide or other alkylene oxides in the form of block polymer chains. Examples include ethoxylated surfactants, cellulose, cellulose derivatives and polyvinyl pyrrolidone components. The alkoxylated (usually ethoxylated) surfactants include, but are not limited to, the group consisting of alkylphenol ethoxylates, ethoxylated fatty acids, alcohol ethoxylates, alcohol alkoxylates, polysorbates (ethoxylated sorbitol) and ethylene oxide-propylene oxide copolymers (commonly called Poloxamers as described in U.S. Pat. No. 5,368,868). A preferred source of iodine for reaction with nonionic materials to form iodine complexes is a composition comprising iodine in association with an inorganic iodide which provides a source of "active" iodine. Such a source is described in Winicov, U.S. Pat. No. 3,028,299, Cantor et. al. U.S. Pat. No. 3,728,449, Schmidt W. et. al. U.S. Pat. No. 5,503,838, Brink et al. U.S. Pat. No. 5,173,291, and McKinzie M. et al., U.S. Pat. No. 5,529,770. Commonly, at least 0.35 parts of iodide (I.sup.-) are present per part of diatomic iodine.
Topical application of biocidal agents has been accomplished using solutions, ointments and physical appliances. To provide prolonged antisepsis, it is usually necessary to repeatedly apply an iodine topical agent since microorganisms may survive the initial application. Topical iodine biocides are usually water soluble which leads to their removal from the epidermis by contact with water or bodily fluids. Increasing the water and bodily fluid resistance of topically applied iodine agents and thereby increasing the substantivity and length of bactericidal activity has been a long-standing goal in the art. This invention teaches against compositions that impart a highly visible iodine coloration to the epidermis such as that derived from complexed iodine and further discloses formulation constraints to provide a persistent non-irritating topical iodine disinfectant that does not stain. Such compositions have several commercially useful properties. The iodine compositions of this invention are not materially affected by water and body fluids and provide long lasting efficacy. Also, the compositions of this application provide iodine in a form that is capable of penetrating the skin and inactivating pathogens that reside within and on the skin.